I m pretty sure Casso would not forgive and forget. As was mentioned above, James Hydell learned how Casso would get even.
I think he would have been successful too because Ruggiero wasn't very sharp and he was careless. Look how he had his daughters phone bugged by the FBI and how he shot off his mouth all the time. And Casso didn't engineer the death of Frank DeCecco. They were after Gotti. Lastly, I don't think Gravano was scared of Casso. He was pretty sharp and was cautious of assassins.